Calculating Latency; Standard Interrupt Latency - Intel 8XC196K Series User Manual

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Calculating Latency

The maximum latency occurs when the interrupt request occurs too late for acknowledgment fol-

lowing the current instruction. The following worst-case calculation assumes that the current in-

struction is not a protected instruction. To calculate latency, add the following terms:

Time for the current instruction to finish execution (4 state times).

— if this is a protected instruction, the instruction that follows it must also execute before

the interrupt can be acknowledged. Add the execution time of the instruction that

follows a protected instruction.

Time for the next instruction to execute. (The longest instruction, NORML, takes 39 state

times. However, the BMOV instruction could actually take longer if it is transferring a large

block of data. If your code contains routines that transfer large blocks of data, you may want

to use the BMOV instruction in your calculation instead of NORML. See Appendix A for

instruction execution times.)

For standard interrupts only, the response time to get the vector and force the call

— 11 state times for an internal stack or 13 for an external stack

The worst-case delay for a standard interrupt is 56 state times (4 + 39 + 11 + 2) if the stack is in

external memory. This delay time does not include the time needed to execute the first instruction

in the interrupt service routine or to execute the instruction following a protected instruction. Fig-

ure 5-2 illustrates the worst-case scenario.

56 State Times

Figure 5-2. Standard Interrupt Response Time

STANDARD AND PTS INTERRUPTS

Interrupt Routine